A U.S. company and its Chinese partner will test electric buses using ultracapacitors that would be chargeable at stops every few miles. The latest ultracapacitors store only 5 percent of the energy that lithium-ion batteries can hold, making them impractical for passenger vehicles. But proponents say the fact that buses have to stop frequently — and at predictable locations — make them a more logical use of the technology. Virginia-based Sinautec Automobile Technologies and Shanghai Aowei Technology Development Company, a partnership that has run 17 similar runs outside Shanghai for the last three years, will test the technology this week at American University in Washington, D.C. Unlike traditional trolleys that stay connected to electric lines throughout their route, there is a collector on top of the Sinautec vehicle that would connect to a re-charging line at bus stops every two or three miles. Within three minutes, banks of ultracapacitors located beneath the seats of the bus would re-charge. “It’s not well suited for electric-only cars,” Joel Schindall, a professor of electrical engineering and computer science at MIT, said of the technology. “But it is practical to stop a bus every few city blocks.” Sinautec officials say each bus requires one-tenth the energy cost of a typical diesel-fueled bus, which would save about $200,000 during the life of the vehicle.